Antenna apparatus

ABSTRACT

First, second, third and fourth dipole antennas ( 14, 16, 18, 20 ) are disposed in a casing ( 1 ). The first through fourth dipole antennas are arranged in the same plane, and are disposed in line symmetry with respect to first through fourth imaginary lines (A, B, C, D) passing through the center of the casing ( 1 ) at an angle of 45 degrees between adjacent imaginary lines.

This invention relates to an antenna apparatus and, more particularly,to an antenna apparatus housed in a casing.

BACKGROUND OF THE INVENTION

An example of an antenna apparatus housed in a casing is disclosed inU.S. Pat. No. 6,498,589 patented on Dec. 24, 2002. The antenna apparatusdisclosed therein includes a main body having a generally octagonalshape in plan, and a lid or cover closing an opening in the main body.Four Yagi antennas are arranged in the main body. First two of the fourYagi antennas are aligned on a first imaginary straight line passingthrough the main body, and exhibit directivities oriented in mutuallyopposite directions along the first imaginary straight line. Theremaining, second two Yagi antennas are aligned on a second imaginarystraight line extending orthogonal to the first imaginary straight lineand exhibit directivities oriented in mutually opposite directions alongthe second imaginary straight line. The second two Yagi antennas aredisposed in a plane at a level vertically deviated from the level of theplane in which the first two Yagi antennas are disposed. Each Yagiantenna includes antenna elements, namely, a radiator, a reflector and adirector, and is disposed within the main body.

The prior art antenna apparatus includes four Yagi antennas so as tohave directivities oriented in different four directions, and each Yagiantenna includes a plurality of elements, such as a radiator, areflector and a director. Four of such Yagi antennas formed of manycomponents must be housed in a single casing, and, therefore, theassembling efficiency is low. In addition, two Yagi antennas must beplaced in one plane, while remaining two must be placed in a differentplane, which further degrades the assembling efficiency.

An object of the present invention is to provide an antenna apparatuswhich can be assembled with improved efficiency.

SUMMARY OF THE INVENTION

An antenna apparatus according to an embodiment of the present inventionincludes a casing, and first through fourth dipole antennas arranged inthe casing. From the point of view of downsizing the antenna apparatus,it is preferred that the casing should be flat. The first through fourthdipole antennas are for receiving radio waves in the same frequencyband. Folded-dipole antennas as well as ordinary dipole antennas may beused.

The first and second dipole antennas are disposed on opposite sides of afirst imaginary line passing through the casing. The distance betweenthe first and second dipole antennas should preferably be not greaterthan a quarter (¼) of the wavelength of the center frequency of thefrequency band to be received by the first and second dipole antennas.Feed points of the first and second dipole antennas are at locations onopposite sides of an intersection of the first imaginary line and asecond imaginary straight line extending orthogonal to the firstimaginary line.

The third and fourth dipole antennas are disposed on opposite sides ofthe second imaginary line, and their feed points are on opposite sidesof the intersection of the first and second imaginary lines. Thedistance between the third and fourth dipole antennas should preferablybe not greater than a quarter (¼) of the wavelength of the centerfrequency of the frequency band to be received by the third and fourthdipole antennas.

The first and second dipole antennas are in line symmetry, with thesecond imaginary line being the axis of symmetry, and the third andfourth dipole antennas are in line symmetry, with the first imaginaryline being the axis of symmetry. The first through fourth dipoleantennas are in line symmetry with third and fourth imaginary straightlines which pass through the intersection of the first and secondimaginary lines at 45 degrees with respect to the first and secondimaginary lines, respectively. The first through fourth dipole antennasare in the same plane, and each may be formed of lines formed on asingle dielectric board or formed of lines formed on two differentdielectric boards.

A directivity adjusting means is disposed in the casing. The directivityadjusting means adjusts the phases and levels of reception signals fromthe first through fourth dipole antennas. (In this specification, areception signal means a signal resulting from receiving a radio wave byan antenna.) The directivity adjusting means makes it possible to changecombined directivities of the first through fourth dipole antennas asdesired.

The directivity adjusting means may include first and second phaseadjusting means level adjusting and combining means.

The first phase adjusting means adjusts the phases of reception signalsfrom the first and second dipole antennas and combines them into acombined signal. In this case, the reception signal from one of thefirst and second dipole antennas may be adjusted to have the same phaseas the reception signal from the other of the first and second dipoleantennas, or the reception signals from both dipole antennas may beadjusted to have the same phase. The phase adjustment and combiningmakes it possible to orient the combined directivity of the first andsecond dipole antennas to a selected one of a first direction along thesecond imaginary line and a second direction opposite to the firstdirection. The second phase adjusting means adjusts the phases ofreception signals from the third and fourth dipole antennas and combinesthem into a combined signal. In this case, the reception signal from oneof the third and fourth dipole antennas may be adjusted to have the samephase as the reception signal from the other of the third and fourthdipole antennas, or the reception signals from both dipole antennas maybe adjusted to have the same phase. The phase adjustment and combiningmakes it possible to orient the combined directivity of the third andfourth dipole antennas to a selected one of a third direction along thefirst imaginary line and a fourth direction opposite to the thirddirection.

The level adjusting and combining means adjusts the levels of outputsignals of the first and second phase adjusting means and combines them,which makes it possible to change the combined directivities of thefirst through fourth dipole antennas as desired. The first and secondphase adjusting means and the level adjusting and combining means aredisposed within the casing.

Since the first through fourth antennas are dipole antennas ofrelatively simple structure and are arranged in the same plane, they canbe assembled in the casing with high efficiency. In addition, since thefirst through fourth dipole antennas are arranged in line symmetry withrespect to the first through fourth imaginary lines, combineddirectivities of the first through fourth antennas can be in symmetry,with the respective imaginary lines being axes of symmetry. Baluns maybe used for coupling the reception signals from the first through fourthdipole antennas to the first and second phase adjusting means. Eachbalun should preferably be at a location on the imaginary line betweenthe two feed points of associated dipole antennas so that it is in linesymmetry with respect to that imaginary line. Also, the baluns for thefirst and second dipole antennas are disposed in line symmetry withrespect to the first imaginary line, and the baluns for the third andfourth dipole antenna are disposed in line symmetry with respect to thesecond imaginary line. This arrangement of the baluns enables the use ofconnecting lines of the substantially same length for connecting thefeed points of the respective dipole antennas, which are in linesymmetry with respect to the first through fourth imaginary lines, tothe associated baluns, so that the phases of the reception signalssupplied to the baluns can match with each other.

Each of the first through fourth dipole antennas may be formed of twoantenna elements, whose innermost end portions are located outward ofthe intersection of the imaginary lines.

The innermost end portions of the antenna elements of the first dipoleantenna may be disposed to intersect those innermost end portions of theantenna elements of the third and fourth dipole antennas which are onthe same side of the first imaginary line as the first dipole antenna isdisposed. The innermost end portions of the antenna elements of thesecond dipole antenna are arranged to intersect those innermost endportions of the antenna elements of the third and fourth dipole antennaswhich are on the same side of the first imaginary line as the seconddipole antenna is disposed. The intersections of the innermost endportions of the antenna elements are on the third and fourth imaginarylines.

With this arrangement in which the innermost end portions of the antennaelements of the first through fourth dipole antennas intersect, the fourdipole antennas can be disposed within a small casing, which downsizesthe antenna apparatus as a whole.

A rectangular substrate on which first and second phase adjusting meansand the level adjusting and combining means are mounted may be disposedin such a manner that the center of said substrate can be located in thevicinity of the intersection of the imaginary lines. The substrate hasits diagonals extending along the first and second imaginary lines, andhas its corners cut away. With this arrangement, the antenna apparatuscan be further reduced in size.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an antenna apparatus according to an embodimentof the present invention, with a lid of a casing and some antennacomponents removed.

FIG. 2 is a bottom plan view of the antenna apparatus shown in FIG. 1.

FIG. 3 is an exploded view of the antenna apparatus shown in FIG. 1.

FIG. 4 is an enlarged perspective view of part of the antenna apparatusshown in FIG. 1.

FIG. 5 is a cross-sectional view along a line V-V in FIG. 2.

FIG. 6 is a block circuit diagram of a directivity adjusting unit of theantenna apparatus shown in FIG. 1.

FIG. 7 illustrates how the directivity of the antenna apparatus of FIG.1 at a frequency of 545 MHz can vary.

FIG. 8 illustrates how the directivity of the antenna apparatus of FIG.1 at a frequency of 581 MHz can vary.

DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION

Referring to FIG. 3, an antenna apparatus according to the presentinvention includes a casing 1. The casing 1 is formed of a main body 2and a lid 4. The main body 2 is formed of, for example, a syntheticresin, and has a generally octagonal shape in plan. The inner bottomsurface of the casing 1 slopes downward from the peripheral portiontoward the center, and is open at one side, e.g. upper side. The openingis closed by the lid 4, which is also octagonal in plan. The lid 4, too,is formed of a synthetic resin, for example, and slopes upward from itsperipheral portion toward the center.

The main body 2 has a bottom wall 2 a and a peripheral wall 2 bextending along the periphery of the bottom wall 2 a, as shown inFIG. 1. As shown in FIGS. 2, 3 and 4, the peripheral wall 2 b includes apair of spaced-apart ends 6 a, 6 a, and also a pair of spaced-apart ends6 b, 6 b. The line connecting the ends 6 a and 6 a orthogonallyintersects the line connecting the ends 6 b and 6 b. Arcuate edgemembers 8 connect adjacent ones of the ends 6 a and 6 b. The ends 6 aand 6 b and the arcuate edge members 8 rise substantiallyperpendicularly upward from the bottom wall 2 a toward the opening andare formed integral with the periphery of the bottom wall 2 a.

The lid 4, too, is formed of a top wall 4 a and a peripheral wall 4 b,as shown in FIG. 3. The peripheral wall 4 b has a pair of spaced-apartends 10 a, 10 a and a pair of spaced-apart ends 10 b, 10 b. The lineconnecting the ends 10 a, 10 a orthogonally intersects the lineconnecting the ends 10 b, 10 b. The peripheral wall 4 b also includesfour arcuate edge members 12 connecting adjacent ones of the ends 10 aand 10 b. The ends 10 a and 10 b and the arcuate edge members 12 risesubstantially perpendicularly from the top wall 4 a and are formedintegral with the peripheral edge of the top wall 4 a.

As shown in FIG. 1, let four imaginary lines A, B, C and D passingthrough the center of the main body 2 be imagined. The imaginary line Apasses through the center of the main body 2 and connects the ends 6 aand 6 a, and the imaginary line B orthogonally intersects the imaginaryline A at the center of the main body 2 and connects the ends 6 b and 6b. The imaginary line C intersects the imaginary lines A and B at thecenter of the main body 2 at an angle of 45 degrees. The imaginary lineD intersects the imaginary lines A, B and C at the center of the mainbody 2 at an angle of 45 degrees with respect to the virtual lines A andB and at right angles with respect to the imaginary line C.

A dipole antenna 14 is disposed within the main body 2, being spaced bya predetermined distance from and in parallel with the imaginary line A.The dipole antenna 14 is formed of first and second antenna elements 14a and 14 b disposed on the same straight line with a spacing disposedbetween their innermost ends. A dipole antenna 16 is disposed in linesymmetry with the dipole antenna 14 with the imaginary line A being theaxis of symmetry. The dipole antenna 16, too, is formed of third andfourth antenna elements 16 a and 16 b having their innermost ends spacedby a predetermined distance along the same line. The first antennaelement 14 a and the third antenna element 16 a face each other acrossthe imaginary line A, and the second antenna element 14 b and the fourthantenna element 16 b face each other across the imaginary line A.

Similarly, a dipole antenna 18 is disposed within the main body 2, beingspaced by a predetermined distance from and in parallel with theimaginary line B. The dipole antenna 18 is formed of fifth and sixthantenna elements 18 a and 18 b disposed on the same straight line with aspacing disposed between their innermost ends. A dipole antenna 20 isdisposed in line symmetry with the dipole antenna 18 with the imaginaryline B being the axis of symmetry. The dipole antenna 20 is formed ofseventh and eighth antenna elements 20 a and 20 b having their innermostends spaced by a predetermined distance along the same line. The fifthantenna element 18 a and the seventh antenna element 20 a face eachother across the imaginary line B, and the sixth antenna element 18 band the eighth antenna element 20 b face each other across the imaginaryline B.

With the imaginary line C as the axis of symmetry, the antenna elements16 a and 18 a are in line symmetry, the antenna elements 14 a and 20 aare in line symmetry, the antenna elements 18 b and 16 b are in linesymmetry, and the antenna elements 20 b and 14 b are in line symmetry.Similarly, with the imaginary line D being the axis of symmetry, theantenna elements 20 a and 16 b, the antenna elements 18 a and 14 b, theantenna elements 16 a and 20 b, and the antenna elements 14 a and 18 bare respectively in line symmetry.

Each of the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 aand 20 b includes two line members formed on a rectangular printedcircuit board by etching. Each of the two line members of each antennaelement includes a line having a length selected for reception of afirst frequency band, e.g. the UHF television broadcast signal band, andan extension which is adapted to be connected in series with the linethrough an electronic switch, such as a PIN diode. The length of theextension is so determined that signals in a VHF high televisionbroadcast frequency band can be received by means of the line and theextension interconnected via the electronic switch. The antenna elements14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 b are disposed such thatthe surfaces of the printed circuit boards are substantiallyperpendicular to the opening of the main body 2.

The distance between the dipole antennas 14 and 16 is shorter than aquarter (¼) of the wavelength A at the center frequency of the UHFtelevision broadcast signal band, which may be, for example, one-eighth(⅛) of the wavelength A. The distance between the dipole antennas 18 and20 is similarly determined, e.g. one-eighth (⅛) of the wavelength A.

The dipole antennas 14 and 16 exhibit an 8-shaped directivity patternalong the line connecting the ends 6 b and 6 b, i.e. along the imaginaryline B. The dipole antennas 18 and 20 exhibit an 8-shaped directivitypattern along the line connecting the ends 6 a and 6 a, i.e. along theimaginary line A. In other words, the directivity patterns of the dipoleantennas 14 and 16 are oriented in a direction different by, forexample, 90 degrees, from the directivity patterns of the dipoleantennas 18 and 20.

The innermost portions of the antenna elements 14 a and 18 b, theinnermost portions of the antenna elements 14 b and 20 b, the innermostportions of the antenna elements 16 a and 18 a, and the innermostportions of the antenna elements 16 b and 20 a intersect each other atassociated ones of first supports, e.g. bosses 22. Four such bosses 22are formed integral with the bottom wall 2 a to extend upward, andsupport the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 aand 20 b.

The antenna elements 16 a and 18 a are described as an example. As isseen in FIG. 4, the innermost portion of the antenna element 16 a isprovided with a slit 100 a extending in the width direction from itsupper edge to a point intermediate between the upper and lower edgesthereof. On the other hand, the innermost portion of the antenna element18 a is provided with a slit 100 b extending in the width direction fromits lower edge to a point intermediate between the upper and lower edgesthereof. The slits 100 a and 100 b engage with each other. The depth orlength of the slit 100 b is equal to the distance of the bottom of theslit 100 a from the lower edge of the antenna element 16 a, so that,when the antenna elements 16 a and 18 a are placed to intersect eachother with the slits 100 a and 100 b engaging with each other, the upperedges of the antenna elements 16 a and 18 a can be aligned with eachother. The other sets of the antenna elements, namely, the antennaelements 14 a and 18 b, the antenna elements 14 b and 20 b, and theantenna elements 16 b and 20 a, are provided with similarly engagingslits and arranged to intersect each other. It should be noted that theintersecting antenna elements of each set are electrically insulatedfrom each other.

As shown in FIG. 4, each boss 22 has a rim including two vertical slits102 a and 102 b located along a line parallel to the imaginary line Aand two vertical slits 104 a and 104 b located along a line parallel tothe imaginary line B. The vertical slits 102 a, 102 b, 104 a and 104 bextend downward from the top to a depth slightly shorter than the widthof the major surfaces of the antenna elements. An opening 106 is formedto extend from the top to a depth at the bottom of the slits 102 a, 102b, 104 a and 104 b, so that the slits 102 a, 102 b, 104 a and 104 b canbe connected together by the opening 106. The intersection of theantenna elements 16 a and 18 a, for example, is inserted into thisopening 106 in such a manner that the antenna element 16 a extendthrough the slits 102 a and 102 b, while the antenna element 18 a extendthrough the slits 104 a and 104 b. The intersections of the otherantenna element sets 14 a and 18 b, 14 b and 20 b, and 16 b and 20 a aresimilarly placed in the openings 106 of the associated bosses 22. Withthe intersections of the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a,18 b, 20 a and 20 b positioned in this manner with respect to therespective bosses 22, the upper edges of the respective antenna elementsare at a level slightly above the level of the tops of the bosses 22.

As shown in FIG. 1, a directive antenna, such as a dipole antenna, 24 isdisposed between and in parallel with the dipole antennas 14 and 16.Similarly, a directive antenna, e.g. a dipole antenna 26 is disposedbetween and in parallel with the dipole antennas 18 and 20. The dipoleantennas 24 and 26 are adapted to receive signals in a second frequencyband, e.g. a VHF low television broadcast frequency band. The antenna 24exhibits an 8-shaped directivity pattern oriented in the direction alongthe imaginary line B, whereas the antenna 26 exhibits an 8-shapeddirectivity pattern oriented in the direction along the imaginary lineA. In other words, the dipole antennas 24 and 26 exhibit directivitiesoriented to directions different from each other by, for example, 90degrees.

The dipole antenna 24 includes first elements 24 a and 24 b. The dipoleantenna 24 includes also second elements 24 c and 24 d disposed withinrespective element cases 28 a and 28 b as shown in FIG. 5.

The first elements 24 a and 24 b each include lines formed on a printedcircuit board by etching. The printed circuit boards are disposed insuch a manner that their surfaces are substantially in parallel with theopening of the main body 2. The first elements 24 a and 24 b aresupported at locations in their innermost end portions by respectivesupports 30 a and 30 b, which are formed integral with the bottom wall 2a and extend upward. Also, the first elements 24 a and 24 b aresupported at their respective outer ends by respective bosses 32 a and32 b, which are formed integral with the bottom wall 2 a and extendupward.

As shown in FIG. 5, the second elements 24 c and 24 d each are formed ontwo printed circuit boards by etching. Specifically, the second element24 c includes two printed circuit boards 34 a and 36 a on which linesare formed by etching. The lines are connected together by a loadingcoil 38 a. The printed circuit boards of the second element 24 c areplaced in the element case 28 a and extend along the length of the case28 a, with their surfaces placed coplanar and in parallel with thesurfaces of the first elements 24 a and 24 b. Similarly, the secondelement 24 d includes two printed circuit boards 34 b and 36 b, on whichlines are formed by etching. The lines are connected together by anotherloading coil 38 b. The printed circuit boards of the second element 24 dare placed in the element case 28 b and extend along the length of thecase 28 b, with their surfaces placed coplanar and in parallel with thesurfaces of the first elements 24 a and 24 b.

As shown in FIGS. 1 and 3, the proximal ends of the element cases 28 aand 28 b enter into the main body 2 respectively through holes 40 a and40 b, formed by hole halves formed in the ends 6 a, 6 a of the main body2 and in opposing ends 10 a, 10 a of the lid 4. The printed circuitboards of the second element 24 c electrically contact the first element24 a on the boss 32 a, and the printed circuit boards of the secondelement 24 d electrically contact the first element 24 b on the boss 32b. Securing means, e.g. screws, are inserted through the bosses 32 a and32 b from under to mechanically couple the second elements 24 c and 24 dto the first elements 24 a and 24 b, respectively.

Annular first ridges 44 a and 44 b are formed around and integral withthe proximal ends of the element cases 28 a and 28 b, respectively. Asis understood from FIG. 1, second ridges 46 a and 46 b protruding inwardare formed around the inner peripheries of the holes 40 a and 40 b. Onlyhalves of the inner peripheral ridges 46 a and 46 b on the main body 2are shown in FIG. 1. With the element cases 28 a and 28 b pushed intothe casing 1 through the holes 40 a and 40 b, the first ridges 44 a and44 b and the second ridges 46 a and 46 b are in surface contact so thatrain or other foreign materials can be prevented from entering insidethe casing 1.

Similar to the dipole antenna 24, the dipole antenna 26 includes firstelements 26 a and 26 b disposed within the main body 2 and secondelements (not shown) disposed within element cases 50 a and 50 b. Thefirst elements 26 a and 26 b, the element cases 50 a and 50 b, and thesecond elements (not shown) are constructed and supported in the samemanner as the first elements 24 a and 24 b, the second elements 24 c, 24d and the element cases 28 a and 28 b of the dipole antenna 24, and,therefore, their detailed description is not given.

A directivity adjusting unit 52 is disposed in the vicinity of theinnermost ends of the first elements 24 a, 24 b, 26 a and 26 b in thecenter portion of the main body 2. The directivity adjusting unit 52includes circuitry for adjusting the phases of reception signals fromthe UHF band dipole antennas 14, 16, 18 and 20. The directivityadjusting unit 52 includes also electronic circuitry for adjusting thelevels of the phase-adjusted reception signals from the UHF band dipoleantennas 14, 16, 18 and 20 or reception signals from the VHF band dipoleantennas 24 and 26, to thereby orient the combined directivity of theUHF band dipole antennas 14, 16, 18 and 20 or the combined directivityof the VHF band dipole antennas 24 and 26, to a desired direction. Thecombined directivities can be oriented to any desired direction by theuse of the directivity adjusting unit 52. The details of these circuitswill be described later.

The directivity adjusting unit 52 is formed on a printed circuit boardarrangement formed of two printed circuit boards, which are disposed oneabove the other, as shown in FIG. 5. The two printed circuit boards aresimilarly formed in a generally rectangular shape, and have theirdiagonals lying on the imaginary lines A and B, as shown in FIG. 1. Thecorners of the two boards are cut away so that the innermost ends of theantenna elements 24 a, 24 b, 26 a and 26 b can be located nearer to theintersection of the imaginary lines A and B, than if the corners of theboards were not cut away.

For directivity adjustment, the reception signals from the dipoleantennas 14, 16, 18 and 20, and the reception signals from the dipoleantennas 24 and 26 are coupled to the directivity adjusting unit 52.Although not shown, transmission lines are provided for the signalcoupling. The transmission lines for coupling the feed points of theantenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 b tothe directivity adjusting unit 52 would be longer if the innermost endportions of the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20a and 20 b did not intersect, which would degrade the VSWRcharacteristic in the UHF band. Longer transmission lines would causethe respective transmission lines to be secured at locationsasymmetrical with respect to each other, causing the electricalcharacteristics of the apparatus unstable. On the other hand, becausethe antenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 bare disposed to intersect the associated ones as described above, thelengths of the transmission lines connecting the feed points of therespective antenna elements to the directivity adjusting unit 52 can bereduced, whereby such problems as described above can be avoided.

For receiving the UHF television broadcast signals by the dipoleantennas 14, 16, 18 and 20, the previously described electronicswitches, e.g. PIN diodes, connecting together the lines and extensionsof the respective dipole antennas are opened, and for receiving the VHFhigh television broadcast signals, the electronic switches are closed.How these electronic switches are controlled is not described in detail.Referring to FIG. 6, the reception signals from the respective dipoleantennas 14, 16, 18 and 20 are coupled, via baluns 200, 202, 204 and 206disposed on the printed circuit board arrangement of the directivityadjusting unit 52, to filter means, e.g. high-pass filters 208, 210, 212and 214, respectively. The baluns 200 and 202 are so arranged that, whensignals in phase with each other are supplied to them, they outputsignals in 180° out of phase. Similarly, the baluns 204 and 206 are soarranged that, when signals in phase with each other are supplied tothem, they output signals in 180° out of phase. As shown in FIG. 1, thebalun 200 is disposed between the antenna elements 14 a and 14 b of thedipole antenna 14, the balun 202 is between the antenna elements 16 aand 16 b of the dipole antenna 16, the balun 204 is disposed between theantenna elements 18 a and 18 b of the dipole antenna 18, and the balun206 is disposed between the antenna elements 20 a and 20 b of the dipoleantenna 20. The baluns 200, 202, 204 and 206 are disposed in therespective corners of the printed circuit board. The baluns 204 and 206are located on the imaginary line A and in line symmetry with respect tothe imaginary line A, and the baluns 200 and 202 are located on theimaginary line B and in line symmetry with respect to the imaginary lineB. The high-pass filters 208, 210, 212 and 214 remove undesiredfrequency components from the reception signals. Output signals of thehigh-pass filters 208, 210, 212 and 214 are coupled to an amplificationand non-amplification switching circuit 240, which is formed ofchangeover switches 216,218,220 and 222, amplifiers 224, 226, 228 and230, and changeover switches 232, 234, 236 and 238, connected as shown.The amplification and non-amplification switching circuit 240 outputsamplified version or non-amplified version of the respective receptionsignals applied thereto via the high-pass filters. When the C/N ratiosof the reception signals are small, the reception signals are amplifiedby the amplifiers 224, 226, 228 and 230, respectively.

The signals as outputted from the amplification and non-amplificationswitching circuit 240, corresponding to the reception signals from thedipole antennas 14 and 16, are applied to a phase adjusting andcombining circuit 242. In the phase adjusting and combining circuit 242,the signal corresponding to the reception signal from the dipole antenna14 as applied from the amplification and non-amplification switchingcircuit 240 is coupled, via a changeover switch 244, either to a firstinput terminal of a combining circuit 246 or to a first end of a phaseshift circuit 248. Similarly, the signal corresponding to the receptionsignal from the dipole antenna 16 as applied from the amplification andnon-amplification switching circuit 240 is coupled, via a changeoverswitch 250, either to the first input terminal of the combining circuit246 or to a second end of the phase shift circuit 248. A second inputterminal of the combining circuit 246 receives, via a changeover switch252, the signal at the first or second end of the phase shift circuit248. The changeover switches 244, 250 and 252 are operated together insuch a manner that, when the changeover switch 244 couples the signalcorresponding to the reception signal from the antenna 14 to the firstinput terminal of the combining circuit 246, the changeover switch 250couples the signal corresponding to the reception signal from the dipoleantenna 16 to the second end of the phase shift circuit 248, and thechangeover switch 252 couples the signal at the first end of the phaseshift circuit 248 to the second input terminal of the combining circuit246. Conversely, when the changeover switch 250 couples the signalcorresponding to the reception signal from the antenna 16 to the firstinput terminal of the combining circuit 246, the changeover switch 244couples the signal corresponding to the reception signal from the dipoleantenna 14 to the first end of the phase shift circuit 248, and thechangeover switch 252 couples the signal at the second end of the phaseshift circuit 248 to the second input terminal of the combining circuit246. The amount of phase shift provided by the phase shift circuit 248will be discussed later.

Similarly, the signals as outputted from the amplification andnon-amplification switching circuit 240, corresponding to the receptionsignals from the dipole antennas 18 and 20, are applied to a phaseadjusting and combining circuit 254. In the phase adjusting andcombining circuit 254, the signal corresponding to the reception signalfrom the dipole antenna 18 as applied from the amplification andnon-amplification switching circuit 240 is coupled, via a changeoverswitch 256, either to a first input terminal of a combining circuit 258or to a first end of a phase shift circuit 260. Similarly, the signalcorresponding to the reception signal from the dipole antenna 20 asapplied from the amplification and non-amplification switching circuit240 is coupled, via a changeover switch 262, either to the first inputterminal of the combining circuit 258 or to a second end of the phaseshift circuit 260. A second input terminal of the combining circuit 258receives, via a changeover switch 264, the signal at the first or secondend of the phase shift circuit 260. The changeover switches 256, 262 and264 are operated together in such a manner that, when the changeoverswitch 256 couples the signal corresponding to the reception signal fromthe antenna 18 to the first input terminal of the combining circuit 258,the changeover switch 262 couples the signal corresponding to thereception signal from the dipole antenna 20 to the second end of thephase shift circuit 260, and the changeover switch 264 couples thesignal at the first end of the phase shift circuit 260 to the secondinput terminal of the combining circuit 258. Conversely, when thechangeover switch 262 couples the signal corresponding to the receptionsignal from the antenna 20 to the first input terminal of the combiningcircuit 258, the changeover switch 256 couples the signal correspondingto the reception signal from the dipole antenna 18 to the first end ofthe phase shift circuit 260, and the changeover switch 264 couples thesignal at the second end of the phase shift circuit 260 to the secondinput terminal of the combining circuit 258. The amount of phase shiftprovided by the phase shift circuit 260 will be described later.

By the use of the phase adjusting and combining circuit 242 describedabove, the combined directivity of the dipole antennas 14 and 16 can beselectively oriented to a direction outward direction from theintersection of the imaginary lines A, B, C and D along the antennaelement 26 a (FIG. 1), which direction is referred to as the forwarddirection hereinafter, and to a direction outward from the imaginaryline intersection along the antenna element 26 b, which direction isreferred to as the backward direction. Similarly, the use of the phaseadjusting and combining circuit 254 makes it possible to selectivelyorient the combined directivity of the dipole antennas 18 and 20 to adirection outward from the imaginary line intersection along the antennaelement 24 b, which direction is referred to as the rightward directionhereinafter, and to a direction outward from the imaginary lineintersection along the antenna element 24 a, which direction is referredto as the leftward direction hereinafter.

Both the dipole antennas 14 and 16 have an 8-shaped directivity. Let itbe assumed that a radio wave comes toward the dipole antennas 14 and 16from the back of the antenna apparatus. A UHF band wave coming from theback is received by the dipole antennas 14 and 16, and outputs aredeveloped at the baluns 200 and 202. The output from the balun 202corresponding to the reception signal from the forward antenna 16 isdelayed by an amount D corresponding to the distance (smaller than aquarter of A) between the dipole antennas 14 and 16, relative to theoutput from the balun 200 corresponding to the reception signal from thebackward antenna 14. The baluns 200 and 202 are so arranged that thephase of the output from the balun 202 is 180°-out-of-phase with theoutput signal from the balun 200. In other words, the output signal ofthe balun 202 has a phase difference of −λ/2−D from the output signal ofthe balun 200. Then, the changeover switches 244, 250 and 252 arecontrolled in such a manner that the output signal of the balun 202 canbe applied as it is to the combining circuit 246, whereas the outputsignal of the balun 200 can be given a predetermined amount of delay ofD1 in the fixed phase shift circuit 248 to thereby have a phasedifference of −D1 relative to the output signal of the balun 202, beforeit is applied to the combing circuit 246. The amount of delay, D1, is sodetermined that the difference between −D1 and (−λ/2−D) can be aboutλ/2. In other words, the delay D1 is set to D. Accordingly, the signalscorresponding to the reception signals from the dipole antennas 14 and16 at the first and second inputs of the combining circuit 246 aresubstantially 180°-out-of-phase, which means that the dipole antennas 14and 16 in combination do not exhibit a backward directivity, but thecombined directivity of the dipole antennas 14 and 16 is oriented to theforward direction.

Conversely, when a UHF band radio wave coming from the forward directionis received by the dipole antennas 14 and 16, the output signal of thebalun 200 corresponding to the reception signal from the dipole antenna14 is delayed by the amount D relative to the reception signal from thedipole antenna 16. By virtue of the different arrangements of the baluns200 and 202, the output signal of the balun 202 is 180°-out-of-phasewith the reception signal from the dipole antenna 14. Then, the outputsignal of the balun 202 has a phase difference equal to −λ/2 from thereception signal of the dipole antenna 14, and the output signal of thebalun 200 has a phase difference equal to −D from the reception signalfrom the dipole antenna 16.

Now, let it be assumed that the changeover switches 244, 250 and 252 areswitched to the positions in which the output signal of the balun 202 isapplied to the phase shift circuit 248, the output of the phase shiftcircuit 248 is applied to the second input terminal of the combiningcircuit 246 and the output signal of the balun 200 is applied to thefirst input terminal of the combining circuit 246. Then, the output ofthe balun 202 is delayed by the phase shift circuit 248 before it isapplied to the combining circuit 246, whereas the output signal of thebalun 200 is applied to the combining circuit 246, as it is. Because theoutput signal of the balun 202 is delayed by an amount of D by the phaseshift circuit 248, the output signal of the balun 202 at the input ofthe combining circuit 246 has a phase of −λ/2−D, so that it's phasedifference from the output of the balun 200 is −λ/2. This causes thecombined directivity of the dipole antennas 14 and 16 to be oriented tothe backward direction.

As described above, the phase adjusting and combining circuit 242 usesthe same phase shift circuit 248 for providing either forward orbackward oriented directivity.

The reception signals from the dipole antennas 18 and 20 are processedin the phase adjusting and combining circuit 254 in the same manner asthe reception signals from the antennas 14 and 16 described above, sothat the combined directivity of the antennas 18 and 20 can beselectively oriented to the rightward and leftward directions. Theamount of delay to be provided by the phase shift circuit 260 is equalto the one provided by the phase shift circuit 258.

As shown in FIG. 6, the reception signal from the dipole antenna 26 iscoupled through a balun 300 to an amplifier 302, where it is amplified.The reception signal from the dipole antenna 24 is coupled through abalun 304 to an amplifier 306, where it is amplified. The amplifiedreception signal from the antenna 24 is applied to a polarity switchingunit 308, which outputs the output signal of the amplifier 306 with thesame polarity as it is applied thereto or with the reversed polarity.

A changeover switch 310 selects either of the output signals of thecombining circuit 246 and the polarity switching unit 308. A changeoverswitch 312 selects either of the output signals of the combining circuit258 and the amplifier 302. The changeover switches 310 and 312 arecontrolled in such a manner as to select either the output signals ofboth combining circuits 246 and 258 together, or the output signals ofthe polarity switching unit 308 and the amplifier 302 together.

The two signals selected by the changeover switches 310 and 312 areapplied to a level adjusting circuit 314. By appropriately selecting thedirectivity of the UHF or VHF high band signal from the combiningcircuit 246 and the directivity of the UHF or VHF high band signal fromthe combining circuit 258 applied to the level adjusting circuit 314,and appropriately adjusting the levels of the signals in the leveladjusting circuit 314 and combining them, the directivity of thecombined signal can be oriented to any desired direction at an anglerelative to zero (0) degree, which corresponds to, for example, theforward direction. Similarly, if the signals applied to the leveladjusting circuit 314 are the VHF low band signals, exhibiting an8-shaped directivity, from the amplifier 302 and the polarity switchingunit 308, a combined signal having an 8-shaped directivity oriented toany desired direction at an angle relative to the forward direction canbe obtained by appropriately selecting the polarities of the signals andappropriately adjusting the levels of the signals in the level adjustingcircuit 314.

For that purpose, the level adjusting circuit 314 includes leveladjusting means, e.g. variable attenuators 316 and 318, and a combiner320 for combining output signals of the variable attenuators 316 and318. Each of the variable attenuators 316 and 318 is arranged toselectively provide an amount of attenuation in multiple steps, e.g.three steps, namely, 0 dB, 7 dB and infinity (∞). The resultant signalcan have a directivity oriented to any desired numbers of directions,e.g. sixteen (16) directions at angular intervals of 22.5 degrees,relative to the forward direction at zero (0) degree. This is achievedby adjusting the directivities and adjusting the amounts of attenuationprovided by the variable attenuators 316 and 318, for a UHF or VHF highband signal, or by adjusting the polarities and adjusting the amounts ofattenuation provided by the variable attenuators 316 and 318, for a VHFlow band signal.

The variable attenuator 316 includes an input-side changeover switch 322connected to the changeover switch 310, and an output-side changeoverswitch 324 connected to the combiner 320. The switches 322 and 324 areoperated together. When the changeover switches 322 and 324 are placedin their first position, the signal as selected by the changeover switch310 is coupled, as it is, to the combiner 320 via the switch 324. Inother words, the amount of attenuation given to the signal is zero (0).With the changeover switches 322 and 324 in their second position, thesignal selected by the switch 310 is attenuated by an attenuatingcircuit 326 providing an amount of attenuation of 7 dB and, thereafter,applied to the combiner 320. In other words, the amount of attenuationof the variable attenuator 316 is 7 dB. When the switches 322 and 324are placed in their third position, they are grounded through matchingresistors 328 and 330, respectively, having an impedance value equal tothe impedance of the respective dipole antennas. Accordingly, the outputsignal from the changeover switch 310 is not coupled to the combiner320. That is, the amount of attenuation is infinite.

The variable attenuator 318 is arranged similar to the variableattenuator 316, and, therefore, no detailed description about it isgiven. It should be noted that the same reference numerals as used forthe components of the variable attenuator 316 are attached to similarcomponents, with a suffix “a” added to the ends of the respectivereference numerals.

Whichever UHF, VHF high or VHF low band signal is to be received, theamount of attenuation given by the variable attenuator 316 is zero (0)for the directivities at zero (0) degree, 22.5 degrees and 45 degrees,but it is 7 dB and infinity for the directivities of 67.5 degrees and 90degrees, respectively. The amount of attenuation for the directivitiesoriented to the directions at 112.5 degrees and 135 degrees is 7 dB, andit is maintained at zero (0) for the directivities of 157.5 degrees, 180degrees, 202.5 degrees and 225 degrees. The amount of attenuation forthe directivities oriented to the directions of 247.5 degrees and 270degrees is 7 dB and infinity, respectively, and the amount ofattenuation for the directivities oriented to the directions of 292.5degrees and 315 degrees is 7 dB and zero (0), respectively. The amountof attenuation is maintained at zero (0) for the directivity of 337.5degrees.

The amount of attenuation in the variable attenuator 318 is infinity, 7dB and zero (0) for the directivities of zero (0) degree, 22.25 degreesand 45 degrees, respectively. It is maintained at zero (0) for thedirectivities of 67.5 degrees, 90 degrees, 112.5 degrees and 135degrees. For the azimuth angels of 157.5 degrees and 180 degrees, theamount of attenuation is 7 dB and infinity, respectively, and it is 7 dBand zero (0) for the azimuth angles of 202.5 degrees and 225 degrees.For the directivities for the azimuth angles of 247.5 degrees, 270degrees, 293.5 degrees and 315 degrees, the amount of attenuation ismaintained to be zero (0), and it is 7 dB for the directivity for theazimuth angle of 337.5 degrees. Like this, when the amount ofattenuation of one variable attenuator is zero (0), that of the othervariable attenuator increases or decreases.

FIGS. 7 and 8 show directivities thus obtained. FIG. 7 shows thedirectivity oriented to various directions at a frequency of 545 MHz,and FIG. 8 shows similar directivity at a frequency of 581 MHz. It isseen from FIGS. 7 and 8 that there are no substantial distortions in thedirectivity pattern in any directions. This is by virtue of thedescribed arrangement in which the dipole antennas 14, 16, 18 and 20 aredisposed in line symmetry with respect to the imaginary lines A, B, Cand D, and the baluns 200, 202, 204 and 206 are disposed in linesymmetry with respect to the imaginary lines A and B. With thisarrangement, the lengths of the lines for connecting the feed points ofthe dipole antennas 14, 16, 18 and 20 to the corresponding baluns 200,202, 204 and 206 can be substantially equal to each other, so that nodifferences in phase are introduced for the antennas 14, 16, 18 and 20,which would otherwise be caused if the lengths of such connecting lineswere different.

As shown in FIGS. 1 and 4, a second support, e.g. a partition 54, isformed within the main body 2 to be integral with the bottom wall 2 a insuch a manner as to surround the directivity adjusting unit 52. Viewedin plan, the partition 54 extends in a generally octagonal shape similarto the shape of the peripheral wall 2 b. The height of the partition 54is substantially the same as that of the peripheral wall 2 b. Aplurality of reinforcing members 56 for reinforcing the partition 54 areformed at intervals on the inner side of the partition 54. Eight (8)slits 108 are formed in the partition 54, which extend from the upperedge down to an intermediate point of the partition 54. Intermediateportions of the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20a and 20 b are placed into the associated slits 108. The depth of theslits 108 is such that the upper edges of the antenna elements 14 a, 14b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 b placed in the slits 108 can bepositioned horizontal, and the width of the slits 108 is slightly largerthan the thickness of the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a,18 b, 20 a and 20 b. The partition 54 contacts the first elements 24 a,24 b, 26 a and 26 b of the dipole antennas 24 and 26 at theirintermediate portions, and, therefore, acts as a support for the antennaelements 24 a, 24 b, 26 a and 26 b. At locations outside and inside thepartition 54, a plurality of drainage holes 58 are formed to extendthrough the bottom walls 2 a.

As shown in FIG. 3, a partition 60 similar to the partition 54 is formedintegrally with the top wall 4 a in the lid 4 in such a location that itcan be positioned outward of the partition 54 when the lid 4 is placedto close the opening in the lower half of the main body 2. The partition60 is formed such that its distal edge can contact the antenna elements,14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 b and the first antennaelements 24 a, 24 b, 26 a and 26 b, when the lid 4 is placed to closethe opening in the lower half of the main body 2. Accordingly, when thelid 4 closes the opening of the main body 2, the antenna elements 14 a,14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 b and the first antennaelements 24 a, 24 b, 26 a and 26 b are placed between and secured by thelower and upper partitions 54 and 60.

As shown in FIG. 3, first pressing members 110 are formed integral withthe lid 4 at locations on the inner surface of the lid 4 correspondingto the bosses 22 on the bottom wall 2 a. These first pressing members110 are formed in a ring shape, as shown, and press down the upper edgesof the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20b at the respective bosses 22 when the lid 4 is placed to close theopening in the main body 2. In this manner, the lid 4 functions not onlyto close the opening in the main body 2 but also to secure the antennaelements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 b in place bypressing them against the bosses 22.

As shown in FIGS. 3 and 5, second pressing members 112, eight in total,are formed on the inner surface of the lid 4 to be integral therewith atlocations corresponding to the eight slits 108 in the partition 54. Whenthe lid 4 is placed to close the opening in the main body 2, the secondpressing members 112 are located inward of the partition 54 and extenddownward from the inner surface of the lid 4 to points by the respectiveslits 108. The second pressing members 112 are tapered, and the portionsslightly above the respective tapered tip ends contact and press theantenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 bagainst one edge, e.g. an outer edge, of the respective slits 108 whenthe lid 4 is placed to cover the opening in the main body 2. When thelid 4 is placed to close the opening in the main body 2, the secondpressing members 112 prevent the antenna elements 14 a, 14 b, 16 a, 16b, 18 a, 18 b, 20 a and 20 b from moving in the slits 108.

In the above-described embodiment, the antenna elements 14 a, 14 b, 16a, 16 b, 18 a, 18 b, 20 a and 20 b of the UHF band dipole antennas 14,16, 18 and 20 are formed separate. However, four printed circuit boardsmay be prepared for the respective antennas 14, 16, 18 and 20, eachincluding two spaced-apart antenna elements lying in line to forms thedipole antenna 14, 16, 18 or 20. In such a case, the dipole antenna 14is arranged to intersect the dipole antennas 18 and 20 at twointermediate points thereof, the dipole antenna 16 is arranged tointersect the dipole antennas 18 and 20 at two intermediate pointsthereof, and the first supports 22 are formed at the respectiveintersections.

In the above-described embodiment, the first pressing members 110 areformed to press down the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a,18 b, 20 a and 20 b against the first supports or bosses 22 at theintersections of the antenna elements, but the first pressing members110 may be arranged to press down the upper edges of the respectiveantenna elements against the first supports 22 at locations other thanthe intersection of the antenna elements. In such case, the upper edgesof the antenna elements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20b may be at a level slightly nearer to the bottom wall 2 a than the topportions of the first supports 22.

The antenna apparatus according to the above-described embodimentincludes both UHF band and VHF band dipole antennas, but it may includeonly dipole antennas for the UHF band. Further, according to thedescribed embodiment, the partitions 56 and 60 are used, but thepartition 60 may be omitted. Also, in place of the continuous partition56, separate supports having the slits 108 may be formed at only thoselocations in the vicinity of intermediate portions of the antennaelements 14 a, 14 b, 16 a, 16 b, 18 a, 18 b, 20 a and 20 b.

1. An antenna apparatus comprising: a casing and first, second, thirdand fourth dipole antennas for receiving radio waves in a same frequencyband; wherein: said first through fourth dipole antennas are positionedin a same plane; said first and second dipole antennas are located onopposite sides of a first imaginary line passing through said casing,feed points of said first and second dipole antennas being located onopposite sides of an intersection of said first imaginary line and asecond imaginary line orthogonal to said first imaginary line; saidthird and fourth dipole antennas are located on opposite sides of saidsecond imaginary line, feed points of said third and fourth dipoleantennas being located on opposite sides of said intersection of saidfirst and said second imaginary lines; said first and second dipoleantennas are disposed in line symmetry with said second imaginary linebeing an axis of symmetry, said third and fourth dipole antennas aredisposed in line symmetry with said first imaginary line being an axisof symmetry, and said first through fourth dipole antennas are in linesymmetry with third and fourth imaginary lines being axes of symmetry,said third and fourth imaginary lines passing through said intersectionof said first and second imaginary lines at 45 degrees with respect tosaid first and second imaginary lines; and a directivity adjusting meansis disposed in said casing, said directivity adjusting means adjustingthe phases and levels of reception signals from said first throughfourth dipole antennas thereby to provide a combined directivity of saidfirst through fourth dipole antennas oriented to a desired direction. 2.The antenna apparatus according to claim 1 wherein said directivityadjusting means including first phase adjusting means adjusting thephases of reception signals from said first and second dipole antennasand combining the phase adjusted reception signals to thereby provide acombined directivity of said first and second dipole antennas orientedeither to a first direction or an opposite second direction, secondphase adjusting means adjusting the phases of reception signals fromsaid third and fourth dipole antennas and combining the phase adjustedreception signals to thereby provide a combined directivity of saidthird and fourth dipole antennas oriented either to a third directionand an opposite fourth direction, level adjusting and combining meansadjusting levels of output signals of said first and second phaseadjusting means and combining the level adjusted signals.
 3. The antennaapparatus according to claim 1 wherein said first through fourth dipoleantennas each comprising first and second antenna elements having theirinnermost portions located outward of said intersections of said firstand second imaginary lines.
 4. The antenna apparatus according to claim1 wherein the innermost portions of said antenna elements of said firstdipole antenna are disposed to intersect the innermost portion of one ofsaid antenna elements of said third dipole antenna on one side of saidantenna apparatus and the innermost portion of one of said antennaelements of said fourth dipole antenna located on said one side of saidantenna apparatus, respectively; the innermost portions of said antennaelements of said second dipole antenna are disposed to intersect theinnermost portion of the other of said antenna elements of said thirddipole antenna on the other side of said antenna apparatus and theinnermost portion of the other of said antenna elements of said fourthdipole antenna on said other side of said antenna apparatus,respectively; and the intersections of said innermost portions of saidantenna elements are on said third and fourth imaginary lines.
 5. Theantenna apparatus according to claim 4 wherein a square substrate onwhich said directivity adjusting means is disposed is positioned in saidcasing with a center of said square substrate positioned at a locationin the vicinity of said intersection of said first and second imaginarylines, and with diagonals thereof extending in line with said first andsecond imaginary lines; said rectangular substrate having its cornerscut away.